Storage and Handling Equipment
A 100,000 barrel crude oil storage tank rupture caused extensive property damage in Dec 1980, in Moose Jaw, Saskatchewan. Failure was attributed to a brittle fracture that originated at a weld between a reinforcing pad and a manway nozzle. Factors that contributed to the brittle fracture included incomplete penetration in a single-bevel groove weld, poor impact properties of the hot rolled ASTM A283 low-carbon steel base material, and air temperature down to 27 C on the day of failure. Details of the analysis and results of impact testing are discussed.
Several newly developed liquid propane gas (LPG) cylinders made from Fe-0.13C-0.42Mn steel failed, each fracturing in the longitudinal direction. One of the cylinders was thoroughly analyzed to determine the cause. Deep-drawing flaws were observed on the inner wall of the cylinder, oriented in the direction of the fracture and roughly equal in length. Flaws about 1.3 mm deep, steps, and a chevron pattern were observed on the fractured surface as were cleavage facets, revealed by SEM. Hardness was relatively high and the microstructure near the fracture surface appeared elongated. In addition, the stress intensity factor KI calculated from the value of the internal pressure was lower than that estimated by the fracture toughness test. All of this suggests that the tanks were not sufficiently annealed and prone to brittle fracture. The analysis thus proves that cracks initiated by deep-drawing flaws were the primary cause of failure.